The purpose of this study was to evaluate the efficacy and tolerability of single-agent gemcitabine in untreated elderly patients with stage IIIb/IV non-small-cell lung cancer (NSCLC). Since April 1997, 46 consecutive patients have been enrolled in this multicenter study. Gemcitabine 1,000 mg/m2 was administered as a 30-minute intravenous infusion on days 1, 8, and 15 every 28 days. Primary patient characteristics were: male/female 38/8; median age 73 years (range: 70-82 years); median Karnofsky performance status (PS) 90 (range: 70-100); stage IIIb 61% and stage IV 39%; histotype: epidermoid 48%, adenocarcinoma 43%, and large cell carcinoma 9%. No complete response was observed, but 10 (21.7%) patients achieved partial response (PR) (95% confidence limits: 11-36%), 27 (58.7%) had stable disease (SD), and 7 (15%) progressed early (at the first evaluation). The median duration of PR and SD was 8 months (range: 4-23+ months) and 4 months (range: 2-9 months), respectively. Subjective response evaluating PS and symptoms such as dyspnea, pain, and cough was evaluated in 40 patients; 11 (27.5%) improved, 15 (37.5%) remained stable, and 14 (35%) worsened. The median time to progression was 4 months, the median survival was 9 months, and 1-year survival was 44%. After a median follow-up of 10.5 months, 14 patients are still alive. There were no grade 4 toxicities. Grade 3 neutropenia and thrombocytopenia occurred in 19% and 2% of patients, respectively. Nonhematologic toxicities were mild. Grade I/II side effects of nausea/vomiting, transient fever, increase of hepatic transaminases, transient peripheral edema at lower extremity (not related to cardiac or renal disease or phlebothrombosis) were reported. This phase II study confirms the activity and favorable toxicity profile of single-agent gemcitabine in the treatment of elderly patients with advanced NSCLC.